Fuel tank cap



FIG. 1 is a perspective view of a fuel tank cap showing our new design;

FIG. 2 is a front view thereof, the rear view being identical to the front view;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof; and,

FIG. 5 is a right side view thereof, the left side view being identical to the right side view.

The broken lines in FIG. 4 are shown for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a fuel tank cap, as shown and described. 